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Bio-based solvents were investigated for the biocatalysed amidation reactions of various ester-amine combinations by Pseudomonas stutzeri lipase (PSL). Reactions were undertaken in a range of green and potentially bio-based solvents including terpinolene, p-cymene, limonene, 2-methyl THF, ɣ-valerolactone, propylene carbonate, dimethyl isosorbide, glycerol triacetate and water. Solvent screenings demonstrated the importance and potential of using non-polar bio-based solvents for favouring aminolysis over hydrolysis; whilst substrate screenings highlighted the unfavourable impact of reactants bearing bulky para- or 4-substituents. Renewable terpene-based solvents (terpinolene, p-cymene, D-limonene) were demonstrated to be suitable bio-based media for PSL amidation reactions. Such solvents could provide a greener and more sustainable alternative to traditional petrochemical derived non-polar solvents. Importantly, once the enzyme (either PSL or CALB) binds with a bulky para-substituted substrate, only small reagents are able to access the active site. This therefore limits the possibility for aminolysis to take place, thereby promoting the hydrolysis. This mechanism of binding supports the widely accepted ‘Ping Pong – Bi Bi’ mechanism used to describe enzyme kinetics. The work highlights the need to further investigate enzyme activity in relation to para- or 4-substituted substrates. A priority in PSL chemistry remains a methodology to tackle the competing hydrolysis reaction.

One common factor across many economies around the world is their high dependency on petroleum. The chemical sector is no exception and considering the paramount role that solvents play within this industry they make an ideal focus for investigating green transition potential. This work attempts to shed some light on the scarce literature regarding the quantitative assessment of substitution capacity in target markets, by examining a case study of toluene use as an industrial cleaning agent and its replacement by limonene, a widely established citrus-peel-derived alternative in a number of applications. The systematic approach presented here compares market demand against potential supply by evaluating current and projected scenarios based on citrus fruit and juice production both at global and regional level. The results clearly show that the potential for complete substitution of toluene by limonene at global level is certainly out of reach, but encouraging results were obtained in specific regional substitution case studies, considering both citrus-producing and citrus-importing countries. In these cases, there is a clear potential for limonene to substitute toluene as a solvent within and beyond the cleaning sector, leaving space for future work in this area to investigate the transition potential for other important bio-based chemicals. © 2016 Society of Chemical Industry and John Wiley & Sons, Ltd

Research into the synthesis and application of green solvents is a developing field of interest relevant to a variety of chemical manufacturers. Tunable solvents utilising carbon dioxide lend themselves to a reduction in work-up solvent and can help avoid the need for energy intensive solvent recovery options such as distillation. This perspective examines the potential benefits of tunable solvents to the chemical manufacturing industry and the environment. Freed from the usual reliance on distillation, high boiling solvents with an inherently lessened potential to cause air emissions can be used as part of a tunable solvent system. The application of bio-based solvents as tunable reaction media is highlighted as an area for further development.

An improved multi-parameter approach to the correlation of enzymatic activity and solvent properties is proposed. The development of the correlation facilitated the introduction of renewable solvents in a CALB catalysed synthesis of fatty esters.

Driven by legislation and evolving attitudes towards environmental issues, establishing green solvents for extractions, separations, formulations and reaction chemistry has become an increasingly important area of research. Several general purpose solvent selection guides have now been published with the aim to reduce use of the most hazardous solvents. This review serves the purpose of explaining the role of these guides, highlighting their similarities and differences. How they can be used most effectively to enhance the greenness of chemical processes, particularly in laboratory organic synthesis and the pharmaceutical industry, is addressed in detail.